Ball chair



FIG. 1 is a side perspective view showing my ball chair design.

FIG. 2 is a front elevation view of my ball chair design.

FIG. 3 is a rear elevation view of my ball chair design.

FIG. 4 is a top plan view of my ball chair design.

FIG. 5 is a side elevation view of my ball chair design; and,

FIG. 6 is a bottom plan view of my ball chair design.

The broken lines shown in the drawings are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a ball chair, as shown and described. 